1. Field of the Invention
This invention relates to a printed circuit board for receiving chip modules and in particular to a circuit board which is configured to receive different chip modules at each chip module site.
2. Description of Related Art
Manufacturers of printed circuit boards typically have to work with a selection of chip modules having different configurations of electrical connectors as well as different arrangements of the electrical connector footprints for connection to the corresponding contacts on the printed circuit boards. As used herein, the terms "contact arrangement" or "connector arrangement" refers to the pattern of the individual connectors or contacts, including the number and location of such contacts or connectors. As used herein, the term "contact configuration" or "connector configuration" refers to the type of physical and electrical connector utilized between the chip module and the printed circuit board, for example, pin grid arrays (PGA), ball grid arrays (BGA), micro BGAs (denser than typical BGAs), column grid arrays (CGA) or direct die attachment. An example of BGA contacts or connectors is the controlled chip collapse connection or C-4 technology which is often referred to in the industry as flip-chip technology. The BGA or C-4 connectors are made of solder balls which electrically and physically connect the chip module to the printed circuit board. CGA connectors are also made of solder, but in a column configuration rather than a ball configuration. Both BGA and CGA connectors must be heated to solder softening temperature in order to make the connection between a chip module and a printed circuit board. On the other hand, PGA connectors utilize pins on the chip module which are removeably received within socket contacts mounted in the printed circuit board. As used herein, "chip module" refers to both single chips to be connected to a circuit board as well as multiple chip arrays mounted on substrate bases, which bases are then subsequently connected to the circuit board.
A microprocessor chip module may be available from one company with PGA connectors and from another company in a BGA package. A board manufacture may want to use either part as a source. However, in order to do this, such manufacturer has had to either manufacture two different circuit boards, one for each of the PGA and BGA packages or, alternatively, build a "daughter" or conversion board to transform either the PGA footprint into the BGA footprint, or vice-versa, at the chip module receiving site on the board. An example of the latter is shown in U.S. Pat. No. 5,515,241. Both of these alternatives involve extra cost to the circuit board manufacturer.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a circuit board capable of receiving different chip modules at each chip module receiving site.
It is another object of the present invention to provide a circuit board which may receive PGA, BGA and/or CGA chip modules at each module site.
A further object of the invention is to provide a combination BGA/PGA/CGA module receiving site which is easier and less expensive to construct on a circuit board.